The present invention relates generally to the manufacture of metal and metal alloy films on electrical components and, more particularly, to apparatus and methods for uniformly depositing or etching thin metal (or alloy) layers on a semiconductor wafer substrate.
Electroplating and electroetching are manufacturing techniques used in the fabrication of metal and metal alloy films. Both of these techniques involve the passage of current through an electrolytic solution between two electrodes, one of which is the target to be plated or etched. The current causes an electrochemical reaction on the surface of the target electrode. This reaction results in deposition on or etching of the surface layer of the electrode. In the plating or etching of thin metal films disposed on a non-conductive substrate, the current tends not to be uniformly distributed over the surface of the target. This non-uniformity is attributed, at least in part, to the so called xe2x80x9cterminal effectxe2x80x9d, i.e., the influence on plating distributions of ohmic potential drop within the thin metal film that acts as an electrode. This effect is exacerbated with increased wafer sizes, decreased seed layer (metallized film) thickness and decreased final deposited layer thickness (often less that 1 xcexcm (micron) in newer designs.
Control of the uniformity of the deposited or etched layer on the target electrode surface (sometimes referred to as the substrate) is particularly important in the fabrication of micro-electronic components. Uniformity is an important consideration when electroplating or electroetching is used to make thin-film electronic components, including resistors, capacitors, conductors, and magnetic devices such as propagation and switch elements. U.S. Pat. No. 3,652,442 issued to Powers et al. and U.S. Pat. No. 4,304,641 issued to Grandia et al. disclose electrolytic processes and apparatus in which alloy and dimensional uniformity are important factors.
In a cup plater, which is often used in the manufacture of small thin-film electronic components, plating uniformity is controlled, to some extent, by system geometry, bath composition, bath flow control, and operating conditions. In one such cup plater (known as xe2x80x9cEQUINOXxe2x80x9d, available from Semitool, Inc.) a baffle, disposed between the target electrode and the counter electrode to affect ion distribution, comprises a plate with a plurality of uniform, and uniformly distributed holes. Nevertheless, a condition known as xe2x80x9cedge effectxe2x80x9d remains a problem. Edge effect manifests itself as the non-uniform thickness that occurs on the edges of a target electrode surface as it is etched or plated.
An object of the present invention is to provide improved electroetching and electroplating apparatus and methods to achieve relatively uniform distribution over the entire surface of an electroetched or electroplated thin metal film, and particularly at the outer edge of the metal film.
To achieve this and other objects, and in view of its purposes, the present invention provides an apparatus and method for an electrodeposition or electroetching system. In accordance with this invention, a thin metal film is deposited or etched by electrical current through an electrolytic bath flowing toward and in contact with a metallized target (or xe2x80x9cwaferxe2x80x9d) on which the etched or deposited film is disposed. Uniformity of deposition or etching is promoted, particularly at the edge of the target film, by baffle and shield members through which the bath passes as it flows toward the target. In general, the baffle/shield combination xe2x80x9cshapesxe2x80x9d the potential field lines next to the target electrode i.e. wafer. The baffle has a plurality of openings disposed to control localized bath flow across the cross section of the bath path. Disposed near the edge of the target, a shield member prevents direct flow of bath toward the edge of the target. Preferably, the baffle causes a proportionately greater rate of current flow toward the center of the target, as compared to that toward the edge of the target, and the shield deflects the current so that the current lines are straight toward the edge of the target.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.